<!DOCTYPE html>
<html lang="en">
  <head>
    <meta charset="UTF-8" />
    <meta http-equiv="X-UA-Compatible" content="IE=edge" />
    <meta name="viewport" content="width=device-width, initial-scale=1.0" />
    <title>Document</title>
  </head>
  <body>
    <script>
      var num = prompt("请输入一个数字");
      // 找因数的个数
      var count = 0;
      for (var i = 1; i <= num; i++) {
        if (num % i == 0) {
          count++;
        }
      }
      // 循环结束
      if (count == 2) {
        alert("是质数");
      } else {
        alert("不是质数");
      }
    </script>
  </body>
</html>
